The invention relates to a method for producing a fiber preform for a fiber composite component, in particular a hollow section, wherein a first fiber structure is braided in a braiding process and a second fiber structure is wound in a winding process.
There are known from the prior art braiding and plaiting processes for producing biaxial and triaxial braids for the production of fiber preforms using different types of fibers, in particular glass fibers, carbon fibers, aramid fibers as well as combinations thereof. The braiding process is particularly advantageous for forming the 0° orientation, that is to say the orientation along the longitudinal axis of the component to be manufactured, even in the case of complex component geometries, because slipping or misalignment of the fibers is reduced through the transverse bonding with braided fibers.
The winding of fibers to produce components is also known in principle from the prior art. However, the winding process is used mainly for rotationally symmetrical components with simple component geometries, because large angles relative to the 0° orientation, that is to say in particular in the circumferential direction, can very easily be achieved by winding, as compared with a braiding process. The 0° fiber orientation can scarcely be produced, or can be produced to only a very limited extent, by the winding process alone.
Braiding methods are likewise subject to limitations as regards variability because, especially in the case of triaxial structures, large angles relative to the 0° orientation can be achieved only with large cross-sections. In addition, the production rate falls considerably in the braiding process in the case of large angles. The fiber material which can be used is also limited by the reel size for the braiding threads and the undulation of the fibers. Fibers with a low thread fineness would have to be used, which increases the costs significantly, in particular when carbon fibers are used.
Against this background, the object of the invention is to provide a method with which there can be produced fiber preforms whose local mechanical properties can be adjusted via the production process.
This and other objects are achieved by a method for producing a fiber preform for a fiber composite component according to the invention, wherein at least a first fiber structure is braided in a braiding process over the entire length of the fiber preform that is to be produced, and at least a second fiber structure is wound in a winding process over a portion of the length of the fiber preform that is to be produced.
In an advantageous embodiment, the winding process and the braiding process take place simultaneously. The fiber preform forms the basis for the fiber composite component that is to be manufactured, wherein the further processing of the fiber preform takes place, for example, by the RTM method. The mechanical properties in the longitudinal direction, that is to say along the 0° orientation, is determined by the braided fiber structure, wherein the transverse mechanical properties can be determined in locally specific regions by the second, wound fiber structure. The component so produced can accordingly meet various requirements. The force absorption and transmission in the longitudinal direction along the 0° orientation is complemented by locally increased force absorption capacities in the transverse direction in the region of the wound fiber structure, for example in order to increase the crash stability of the component in the transverse direction. In order that the weight and the costs of the component are not increased excessively, it is provided according to the invention that the process of winding the second fiber structure does not begin until the first fiber structure has already been braided over a predetermined length in the braiding process, so that the fiber preform to be manufactured is provided with the wound fiber structure only in the region in which it is actually required, and the locally increased force absorption capacities in the transverse direction are achieved only in that region. This efficient use of the fiber material limits the material-related costs and reduces the weight of the fiber preform that is to be manufactured.
It is advantageously further provided that the winding process is integrated into the ongoing braiding process and terminated from the ongoing braiding process. To that end, the winding unit can be integrated into the braiding machine and can be so configured that the fibers can locally be applied to and removed from the fiber preform to be manufactured. The manufacturing installation advantageously has special pressure rollers for that purpose, with which the fiber structure to be wound is pressed onto the fiber preform until the friction between the fibers is sufficient that they fix themselves independently. In order to terminate the wound fiber structure, the fibers are cut with a cutting blade and attached to the fiber preform by the pressure rollers. To that end, it is provided in one embodiment of the invention that the fiber ends are fixed to the component to be manufactured by the action of heat and by a type of adhesive (e.g. spray adhesive, adhesive tapes, etc.). For example, the pressure rollers can be correspondingly heated for that purpose and equipped with a spray-adhesive device. Fixing accordingly takes place by the activation of binders previously introduced into the fibers. It is further possible to use the so-called fiber placement method.
The braiding process is not limited to a fiber orientation of 0°, it is also possible to braid fiber orientations of ±45°, wherein the winding process is additionally integrated with even larger angles. The fiber orientation of the wound fibers is in a range of from ±30 to ±80°, in particular from ±45 to ±80°. In an embodiment that is advantageous in terms of the production rate, the braided fibers are used for the 0° orientation and the wound fibers are used for a fiber orientation of from ±30 to ±80°. Positive and negative fiber angles are each adjusted through the direction of rotation of the winding.
The scope of protection of the present invention also includes the fiber preform for a fiber composite component having a first fiber structure extending over the entire length of the fiber preform and braided in a braiding process, and a second fiber structure extending over a portion of the length of the fiber preform and wound in a winding process. In an advantageous embodiment, the first fiber structure is triaxially braided and forms the 0° orientation. The wound fiber structure is arranged in a locally limited manner and has angles of from ±30 to ±80° relative to the 0° orientation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
The figures are schematic and by way of example. In all the views, the same reference numerals denote the same components.